The date of publication for this week’s edition of Shares - Thursday 17 September - is quite possibly been ringed in red in the diaries of many economists and currency traders. This is when we hear the latest pronouncement from the US central bank, the Federal Reserve, on monetary policy and interest rates. Apart from the slowing down of China, exactly when the US would pull the trigger on raising rates has been the main concern for markets for some time now and, earlier this year, September was the best 'guesstimate'.

But as is often the case with deadlines financial, this has changed. At the time of writing the market was pricing in only around a 30% chance of a rate rise this month. Most people though do still think it will happen this year, with December the current favoured month.

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So what effect is this likely to have on the US dollar? First of all, whether it is September or December or somewhere in between, the market is definitely pricing in a rise in American interest rates this year. Whenever it comes, it is expected - although the timing as to which actual month it happens in could definitely provide some short term volatility. Markets are not expecting a large move - a 0.25% hike in rates is the almost certainly the biggest move the US will make.

What is probably going to be more important when this interest rate rise comes out is the dialogue around it from the Federal Reserve chair, Janet Yellen. What she says in the press conference will be pored over and dissected for quite some time. If you think when the rate rise happens that’s the end of speculation about interest rates - think again. The game then will be to figure out just how fast the next one is coming and just how high rates could go.

There have already been cautionary noises from the likes of the International Monetary Fund and the Bank of International Settlements (BIS) about the impact a rise will have on a fragile world economy. The BIS - referred to by some as the bank of central banks - have warned that debt ratios are at extreme levels in all sorts of economies around the world and even a small rise in rates would leave the global economy acutely vulnerable to shocks. But many people do feel rates have to go up - and should have gone up long before now - because if world economies need some sort of stimulus further down the line, rates can hardly be cut much lower.

Back to how the US dollar may move. If markets thought the first rate rise was the sign of even more to come, it would be dollar positive. One thing that can drive currencies higher is the interest rate, making it a more attractive place to park your money. But, given some of the rumblings seen in various markets lately, it seems unlikely we are going to see a series of swift rises from the Fed.

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As every currency trader and his dog seems to be expecting rates to rise this year, when the news is finally out we could actually see US dollar weakness. It is a variation on the old adage of 'buy the rumour, sell the fact' occasionally quoted for stock markets. A market rises in anticipation of good news and when the news is out everyone who wants to buy has bought - and there is only one way for it to go. So barring any aggressive outlook from the Fed about any more imminent rises, buying the likes of the euro and the pound against the dollar could well be the more sensible medium term position here.